/*
  shader 绘制
  2 gbuffer
  生成好多线段
  线段排序
  每一点和线段比较
  距离0 - 0.5 => 1 - 0.5
  0 -> 0
  .5 -> 1/3
  1 -> 1/2
  ax*x + bx + c = y
  c = 0 !!!!!!!!
  1/4 * a + 1/2 * b = 1/3
  a + b = 1/2
  1/2 * a + b = 2/3
  1/2 * a = 1/2 - 2/3 = -1/6
  a = -1/3 !!!!!!!!
  b = 5/6 !!!!!!!!
*/















